TFXX /F111 Page 3

How the body evolved

It is not my intent to show how the entire configuration developed, but the airplane was , in my opinion, determined by the criticality of the high speed dash mission. This set limits on just how large the maximum cross section area could be.

Everything else being equal, for supersonic flight the most critical element is the maximum frontal area and the change in shape along the length of the airplane.. This is not so for subsonic flight where total wetted area is just as important. For a body of revolution there is a theoretical shape that provides the minimum wave This is referred to as a Sears-Haack body. Of course the real airplanes are much more complex shapes than a simple body of revolution, like a missile, but the concept of Sears-Haack requires the cross section areas to change smoothly along the length of the body.

This applies not only to the body of the airplane, but to the wings and empenage. The figure below first shows a typical cross sectional plot of an airplane and wing combined. Next to it the body has been area ruled, that is reduced in cross section where the wing joins the body. The result is the curve has been smoothed out and the maximum cross section reduced in value. A number of airplanes in the early 1950’s ,like the F11 and the F106, used this concept to reduce drag particularly in trans sonic flight.

Of course there is a limited amount of “area-ruling” that can be done depending on the unique requirements of the design. For the TFX, the important considerations were to minimize the maximum cross sectional area and to do what ever could be done to keep the plot of the area as smooth as possible. .

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It was believed ( prior to wind tunnel testing) the maximum cross section area would have to be below some value that I have long since forgotten, but lets say about 48 square feet for illustration purposes. Now this is not just the body, but also includes the wings, and further the area distribution had to be smooth.

This was a continuous design process. There must have been hundreds of these plots made as all the airplane parts were added.

What determined the minimum area needed.

Once the crew station, nose radar, the engine and inlets ,and the bomb bay were configured, all that was left was the landing gear. All those things above pretty much determined just how much space was available for the landing gear. Fitting the main landing gear into the little area that was left for it was the most difficult problem in the whole design

Layout after layout was made trying all kinds of schemes to get a usable landing gear in the available space. As I recall both GD and Grumman engineers gave it a try, until one General Dynamics designer came up with what he called the “fomoco “ gear. Fomoco derived from Ford Motor Company. He said it was the Ford front wheel suspension system that gave him the idea!

Now I believe there are (or were some44 years ago) no better landing gear designers in the world than at Grumman, considering carrier landings. But there never would have been a F111 without his ‘fomoco’ design.

Interestingly, for all production airplanes the landing gear was supplied by Grumman.

During the proposal there was a continual update on just how well the General Dynamics TFX was meeting the Mach 1.2 dash mission of 200 miles.

Rumors had that Boeing was having troubles and was only making about 150 miles. I believe we thought the GD design would guarantee 190 miles or so/

Just a few days ago I found a wonderful story on the internet providing a complete and accurate history of the TFX program. It is the work of George Spangenberg who was the director of new aircraft evaluation for US Navy. Although I never actually met him, we designers knew it was he we had to convince more than any one else in Defense Department iif we were going to get the contract award. Now it is also true that he clearly thought that Boeing should have been selected for the TFX, but was overruled by a whole bunch of politicians including, of course Lynden Johnson.

If you read through this reference you will see the complete story of the program with just about all the pertinent statistics of the TFX story .

TFX/F111 Page 2

As you can see right from the beginning these two requirements would be hard to do with a single airplane configuration.

In addition the AF airplane basic weapon system required a missile or bomb to be carried in an internal bomb bay. The Navy weapon system was the Phoenix system that required six external missile launch positions. There was no way to carry the Phoenix missiles in the limited space of the internal bay.

Ok, the above requirements are not totally impossible for a single design to handle, but there is still a lot more to consider.

The most difficult thing is the basic size of the aircraft. For the AF if the airplane grows a little, no problem we need a little longer runway. If it gets a little heavy, we increase tire size etc.

However the Navy airplane must operate off an aircraft carrier. Now the Navy said it must not exceed 55,000 pounds gross weight, and 56feet in length with a span shorter than x feet with the wings folded or in this case retracted.

I don’t mean to overlook the tremendous effort made by GD and Grumman in proposing an airplane that can fly at mach 1.2 on the deck for almost 200 miles, and still be able to loiter for a few hours at 30000 feet while protecting the fleet with phoenix missiles, but the Navy version (F111B) was simply too heavy.

When the fourth proposal was about to be submitted the fall of 1962 a huge argument developed at Fort Worth. Grumman weights engineers came up with a gross weight estimate for the B version of approximately 65,000 pounds.

As I recall General Dynamics weights reviewed the data that night and announced in the morning that their estimate was close to 60,000 pounds.

Grumman management backed the Grumman engineers and said Grumman could not support the proposal submittal, and sent every body on the Grumman team home. (Grumman had a team of bout 20 engineers working there in Fort Worth as part of the proposal effort)

Now I don’t want to suggest GD was fudging the numbers, but let us remember the final gross weight of the actual F111b was about 78,000 pounds.

I wasn’t back at Bethpage (the Grumman facility) for more than one day when I was called by the chief engineers secretary and told to get back to Fort Worth immediately. What happened was Grumman management agreed to keeping our name on the proposal , but words were added showing our reservation as regards the B model gross weight.

The Proposal Effort

There were many interesting events during the proposal efforts worth discussing that provide insight of how this airplane evolved.

First, there were two separate groups of engineers: the Texans and the Yankees ( actually the NY Yankees) One group dedicated to the Air Force and the other to the Navy.

However that was never a problem as we worked together very well.

The real problem was getting an overall configuration to contain all the equipment able to do the job and still fit on an aircraft carrier.

Let me explain. The most critical requirement was imposed by the AF need for the Mach1.2 200 mile dash on the deck. As I recall there were no airplanes or very few flying that had ever exceeded Mach 1.0 at sea level. The TFX would do it at Mach 1.2 and for 200 miles!

So it was obvious this design had to have minimum frontal area. However the AF also required the airplane to be able to land on relatively soft terrain. I believe it had to be as soft as a UCI (Unit Construction Index)of around 5. Now don’t ask me why the AF needed to operate on such soft ground.

The Navy on the other hand was dealing with a steel carrier deck and could use extremely high tire pressure.

So the AF airplane gets huge tires and that kind of establishes just how big the body is going to be. Oh, I forgot the airplane is also a variable sweep wing design. The landing gear has to be stowed in the body. Add to the above the need for weapons storage, room for the large Phoenix system radar, and a side by side seated crew system, and you begin to see the design challenges.

(By the way, the only non-experimental variable sweep wing design ever built prior to the TFX was the Grumman F10F-1 Jaguar.( First flight May 19,1953) Unfortunately the 10F was ,to say the least, not a very good airplane. But the mechanics of the sweeping wings and the body mounted landing gear were excellent. That was the first airplane I worked on when I started at Grumman in 1950)

F10F-1 taking off at Muroc CA in 1953 . Click on image fo a larger view

The TFX story page 1

THE TFX STORY- the F111a and f111b

The Request for Proposals begin

In the last few months of the Eisenhower administration the Air Force began to argue that it needed a successor for its F-105 tactical fighter. This became known as the TFX/F-111 project. However Robert McNamara (then Secretary of Defense) changed the TFX from an Air Force program to a joint Air force/Navy under-taking.

On October 21, 1961 the two services sent the aircraft industry the request for proposals for the TFX with instructions to submit the bids by 1^st December 1961.

Six bids were received from Lockheed, North American, Boeing, Republic/Vought.\, General Dynamics/Grumman, and McDonnell/Douglas.

Thus began the larges most expensive airplane program in our history. Before the final award was made to General Dynamics/Grumman in November 1962 there were 3 additional rounds of proposal submittals.

This story is told from the point of view of the US Navy and Grumman. General Dynamics realizing it had no real experience with Navy fighter aircraft decided to team with Grumman for this bi-service effort. I was on the team sent by Grumman to Fort Worth to work with the General Dynamics team. Our main interest was to insure the final product would meet all of the Navy requirements without compromise imposed by the dominant Air Force mission.

Of the six original proposals Boeings design was clearly the best, although the General Dynamics /Grumman proposal was considered acceptable. The others were rejected for various reasons.

Without trying to describe the complex politics involved the decision was made by the evaluators to have Boeing and General Dynamics/Grumman both submit revised proposals addressing some unresolved question. That and two more proposals were submitted until the last proposal was received in September 1962.

The Basic Requirements-What made the TFX so difficult to develop

When McNamara combined the Air Force and Navy requirements in to one common vehicle it almost guaranteed a bad outcome. Boeing met these requirements by proposing two not really common designs, where as GD/Grumman maximized the commonality as much as possible.

First, let me explain the critical requirements for both .What designed the AF airplane was a mission for the aircraft to fly a long distance at altitude then descend to sea level and dash 200 miles to the target at a speed of mach1.2.

For the Navy the airplane was designed for carrier task force defense.

This meant it would have to cruise a several hundred mile distance from the fleet and then loiter at altitude to establish a defensive position to destroy any enemy aircraft before it could threaten the fleet.

Grumman History

This diagram shows the rather large number of products produced by Grumman with a diversity ranging from aerospace to a ocean research.The time period is from 1930 through early 1970. Those were the days when there was less reliance on computers and when small companies were able to do so much in so little time.
Between 1965 and 1970 Grumman had the F111b, the Gulfstearm II, the OV-1D,the F14,the Flagstaff hydrofoil, the EA6b,the LEM, and the PX15 submersible all in development at the same time!

Grumman Design 134 Tilt wing Mohawk

en route to Alaska ,summer of 1959

gulfstream start

There are a bunch of similar stories yet untold about many airplanes that I think might interest your readers. For example, Nancy Pelosi's airplane needs: As you know the AF has suggested using a military 767 instead of the Gulfstream 500 (C37a ) that Denny Hastert used. I am pretty familiar with both of these aircraft having worked on development of each. The C-37a has range of 6300 miles range and is certainly able to fly from DC to San Francisco.

 

In fact the Gulfstream 500 is the probably the best executive airplane ever built(I flew on  the first Jet Gulfsteam G2 to Denmark in 1976 when we were trying to sell planes to the Danish Air Force. In those days twin engine airliners were not approved for transatlantic flights. FAA part 135 regulations  required twin engine aircraft to be within 90 minutes of an airfield in the event of a single engine failure. During the 80's Boeing got relief from this requirement by establishing improved engine and systems reliability. Both 767's and 757's now routinely fly transatlantic and other long over water flights("ETOPS" Extended-range Twin-engine Operations permit qualified aircraft to be as far as 180 minutes from an emergency landing field)

 

Well whether the speaker of the house really needs a 767 instead of the world's classiest executive airplane we will wait and see.

But what few people know is the history of the Gulfstream airplane creation. The series of airplanes now totaling about 800 ( I may be incorrect) all started back in 1956 when the Grumman Mohawk left preliminary design and began actual development. I was working in PD(preliminary design)and needed something to do  as our work on the Mohawk was done. This was the era of converting war surplus airplanes into business transports, like the C47s used by many company's like Exxon, Shell, Kodak, IBM, Sperry, AT&T for example. Grumman had built the Mallard amphibian as fill in job at the end of WW2 and founder Leroy Grumman thought it would be good to design a brand new executive airplane in as much as the fleet of old C47s were not very fast and could not fly over the weather.

 

However we in PD started originally on a turboprop version of the C1A carrier born utility transport. They never told us what Leroy really wanted, and he was on vacation in Florida. So I worked on how we could replace the piston engines with Lycoming T55 turboprops. Well lots of things had to change. First the fuselage had to be made circular in cross section so it could be pressurized. And while we were at it, a new wing was required for the turboprops. Ok we could do that, but now we needed a much longer landing gear because the props were so big. Well my boss Mike Pelehack (later to become president of Grumman)insisted we could adopt the existing C1A gear. I made design  study after design study, but could not convince him that it could not be done. That all ended when we finally were told that they didn't really want a new carrier airplane but an executive transport!

 

Then began the first layouts of what was eventually to become the Gulfstream series of great airplanes. This is the beginning of a really interesting story, which includes how the airplane became a low wing design and how Grumman commissioned a market survey to see how a brand new airplane would sell.( you would not believe the result of the survey and the decision to go ahead with the program)